1. Field of the Invention
The present invention relates to an electromagnetic steel sheet having excellent magnetic properties, preferably to an electromagnetic steel sheet for application as a magnetic core, and a production method thereof.
2. Description of the Related Art
It is preferable that an electromagnetic steel sheet (silicon steel sheet) has a texture such that the electromagnetic properties in the magnetization direction in use can be excellent. A preferable texture varies depending upon the application. However, for an EI core, which has the magnetization directions orthogonal to each other, a so-called cubic texture with a {100} rolled face orientation and a  less than 100 greater than  rolling orientation (RD) is most preferable.
In order to obtain such a texture, various methods have been advocated so far.
Examples thereof include a melt quenching method disclosed in the official gazette of Japanese Unexamined Patent Publication No. 5-306438, a cross rolling method disclosed in the official gazette of Japanese Unexamined Patent Publication No. 5-271774, a tertiary recrystallization method disclosed in xe2x80x9cGrowth of (110)[001]-Oriented Grains in High-Purity Silicon Iron-A Unique Form of Secondaryxe2x80x9d (TRANSACTIONS OF THE METALLURGICAL SOCIETY OF AIME, VOL 218, 1960 P. 1033-1038), and a columnar crystal growth method disclosed in the official gazette of Japanese Unexamined Patent Publication No. 62-262997.
However, since all of the above-mentioned methods excluding the melt quenching method depend on cold rolling and annealing, a complicated process is required as disclosed in the official gazette of Japanese Unexamined Patent Publication No. 4-346621. Further, the melt quenching method requires a special cooling roller. Therefore, in either of the methods, high production costs have been problematic.
On the other hand, a grain oriented silicon steel sheet is known as an expensive electromagnetic steel sheet. The grain oriented silicon steel sheet has a texture having a so-called Goss orientation, {110} less than 001 greater than  orientation in the vicinity of the surface layer of the hot rolled steel sheet in a small amount so that secondary recrystallization can be conducted, utilizing the Goss orientation grains. The magnetic properties thus obtained are superior in the rolling direction (RD), but inferior in the transverse direction (TD).
It has been a common view that Si is superior to other alloy elements from the comprehensive aspect although some elements are superior to Si in one of the characteristics including magnetic and mechanical properties, in particular, processability and alloy cost. However, the present inventors elaborately studied the application of the alloy elements other than Si into an electromagnetic steel sheet and discovered that an electromagnetic steel sheet with an Fexe2x80x94P composition can obtain properties superior to those of a silicon steel sheet as disclosed in of Japanese Unexamined Patent Publication No. 9-41101.
An object of the present invention is to provide an electromagnetic steel sheet having a texture that is highly integrated in the {100} less than 001 greater than  orientation, at a low cost, all without the need of a complicated process.
A further object is to create a method of making such an electromagnetic steel sheet.
We have discovered that the texture of steel having a specific resistivity of about 15 xcexcxcexa9xc2x7cm or more can be improved by applying sufficient strain at a high temperature, and by large reduction in hot finish rolling, step compared with the conditions adopted in the conventional process. The steel sheet of this invention is extremely effective for the targeted objective.
Preferred configurations of the present invention include the following embodiments:
1. An electromagnetic steel sheet having excellent magnetic properties, with about a 15 xcexcxcexa9xc2x7cm or more specific resistivity, about a 2.0 {100} less than 001 greater than  integration degree/{as a ratio to the 111} less than uvw greater than  integration degree, and has about a 10 xcexcm to 500 xcexcm grain size.
2. The electromagnetic steel sheet described in paragraph 1, wherein the steel sheet composition contains about 0.1 to 3.5% by weight of Si and the {100} less than 001 greater than  integration degree is about 10 or more.
3. The electromagnetic steel sheet described in paragraph 1, wherein the steel sheet composition contains about 0.2 to 1.2% by weight of P, and wherein the {100} less than 001 greater than  integration degree is about 3 or more.
4. A production method of the electromagnetic steel sheet described in paragraph 1, wherein a large reduction ratio is applied to a steel slab in the vicinity of the final stage of a hot rolling process, with the components adjusted such that the specific resistivity of the product is about 15 xcexcxcexa9xc2x7cm or more and the hot rolling finishing temperature is about 750 to 1150xc2x0 C.
5. A large strain, as described in paragraph 4, can inlude specifically a rolling operation in the hot rolling final pass, with about a 30% or more reduction ratio. In addition, the operation can include conducting finish rolling in the hot rolling process with 1 pass. Or the large strain described in paragraph 4 can include an operation with about a 50% or more hot rolling final 3 passes accumulated reduction ratio and about a 10% or more final pass reduction ratio.
6. A steel slab with the components adjusted such that the specific resistivity of the product can be about 15 xcexcxcexa9xc2x7cm or more made according to the method described in paragraph 4, the steel slab containing about 0.1 to 3.5% by weight of Si, or about 0.2 to 1.2% by weight of P.
7. The production method of an electromagnetic steel sheet described in paragraph 4, wherein the slab is made from a component having a ferrite-austenite transformation at about 750 to 1150xc2x0 C. and wherein and the hot rolling finishing temperature is Ar1-100 to Ar1+50xc2x0 C.
8. The production method of an electromagnetic steel sheet described in paragraph 4, wherein the slab is made from a component to have a ferrite single phase at about 750 to 1150xc2x0 C. and the hot rolling finishing temperature is higher than or equal to 1010+100xc3x97[Si]xe2x88x925xc3x97reduction ratio of the final hot rolling pass (%).
In general, a steel slab (about 10 to 500 mm thickness) reheated to about 900 to 1450xc2x0 C. is processed into a hot rolled steel sheet having about a 0.8 to 4.0 mm thickness by hot rolling. Usually the slab is processed to the form of a sheet bar having about a 15 to 50 mm intermediate thickness before converting the bar to the state of the hot rolled steel sheet. The hot rolling operation from the slab to the sheet bar denotes a rough rolling and the hot rolling operation from the sheet bar to the hot rolled steel sheet denotes a finish rolling. In some cases, a direct rolling operation without reheating the slab, or a finish rolling by directly casting the sheet bar can be conducted. The expression xe2x80x9cvicinity of the final stage in a hot rolling processxe2x80x9d according to the present invention refers to the stage from the final pass of the hot finish rolling to one or several passes before the final pass. Further, the expression xe2x80x9cAr1 (xc2x0 C.)xe2x80x9d refers to the temperature achieving the ferrite single phase from the (ferrite+austenite) phase in the cooling of the steel.
According to the present invention, a steel sheet having a cubic texture, having excellent magnetic properties, can be provided by conducting hot finish rolling at a high temperature and providing large reduction, with the subsequent cold rolling process and the annealing process conducted in an ordinary manner without the need of a special condition. The resulting steel sheet can be produced at a cost that is drastically lower than conventional steel sheet.